This invention relates generally to a novel method and apparatus for measuring the amount of carbon and other organics in an aqueous solution. More particularly, this invention concerns a novel multistage reactor and method for irradiating an aqueous solution with ultraviolet radiation. Oxygen is introduced into the solution; and the solution and oxygen are brought into direct contact with an ultraviolet lamp in each stage of the reactor. The solution enters the lower portion of the reactor stages and exits the upper portion of each stage. The multistage reactor provides a facility for optimizing a desired chemical reaction out of several competing reactions, while reducing interferance from unwanted reactions. Testing need not be done on a batch basis; processing may proceed on a continuous basis.
In the past, it has been common to require a combustion step at high temperatures. Measurements have been performed by introducing a sample and air or oxygen at a measured rate into a metal reactor, or a quartz tube filled with a catalyst, which is running at a temperature typically between 760.degree. C. and 900.degree. C. Carbon in the sample is oxidized to carbon dioxide and then passed through a condenser to remove water from the system. The gas is then passed to a conventional carbon dioxide detector.
Such prior art high temperature methods have proven to be unsatisfactory because of the long response times required. Such prior art methods have proven to be extremely slow and combersome. Such methods are also succeptible to catalyst poisoning, and are generally incapable of adequately handling salts in solution in the sample to be tested.
Batch systems employing ultraviolet radiation to oxidize carbon in a sample solution are known.
One such system is disclosed in U.S. Pat. No. 3,958,941, issued May 25, 1976, to Michael Daniel Regan. Regan discloses an ultraviolet lamp 3 internal to a single stage irradiation chamber 1. Regan requires the carrier water to be absolutely pure. The Regan device requires a time consuming special cleaning cycle during which water valve 25 is opened to allow the carrier water to be circulated through a mixed bed ion exchange cartridge 27 to remove ions which might interfere with the desired reactions. After the cleaning cycle, the valve 25 is closed. A known volumn of sample, typically one milliliter, is introduced into a first water loop 9 via a sample input port 35.
An air loop 31 passes air through the top of the irradiation chamber 1. Regan also teaches that water and air is to be pumped into the top of the irradiation chamber 1, and that the water should exit through the lower portion of the irradiation chamber 1. Regan teaches that the air loop 31 is to isolate non-gaseous substances contained within the sample from the measuring chamber 11.
The Regan device is unsatisfactory and slow in that it requires a preliminary cleaning cycle to insure that the water is absolutely pure. The Regan single stage irradiation chamber is incapable of optimizing the desired reactions in order to overcome interference from undesired reactions. The Regan device is limited to batch testing, and is incapable of continuously processing sample solutions. Regan also does not appreciate, and fails to teach or suggest, that oxygen should be introduced into the sample prior to ultraviolet irradiation, and that the oxygen and water mixture should be introduced into the lower portion of the reactor in order to realize certain advantages, as set forth more fully below.
The problems enumerated in the foregoing with respect to the above prior art systems are not intended to be exhaustive, but rather are among many which tend to impair the effectiveness of previously known devices and methods for measuring organics in an aqueous solution. Other noteworthy problems may exist; however, those presented above should be sufficient to demonstrate that devices and methods for measuring organics in an aqueous solution appearing in the prior art have not been altogether satisfactory.